https://amsterdamassassin.wordpress.com/2018/12/16/typecast-my-royal-fp-steampunk/

https://www.amsterdamtypewriter.com/en-us/products/typewriter-key-inserts-universal?variant=49394561876302&_pos=1&_psq=glass+key&_ss=e&_v=1.0

Amsterdam Typewriter began selling these around 2024-09-24: https://www.facebook.com/groups/typewritermaintenance/posts/3869850413252379/

One set consists of 45 normal keys (12.2mm) + 4 shift keys (16.2mm)

https://www.amsterdamtypewriter.com/en-us